Swine flu (H1N1)

"Swine flu" was the popular name for flu caused by a relatively new type of flu virus responsible for a global flu outbreak (or pandemic) in 2009-10. It's now just a normal type of seasonal flu and is included in the annual flu vaccine.

The scientific name for the swine flu virus is A/H1N1pdm09 – sometimes shortened to "H1N1".

"Swine flu" pandemic 2009-10

The virus was first identified in Mexico in April 2009. It became known as swine flu because it's similar to flu viruses that affect pigs.

It spread rapidly from country to country because it was a new type of flu virus that few young people were immune to.

Overall, the outbreak wasn't as serious as originally predicted, largely because many older people were already immune to it. Most cases in the UK were relatively mild – although serious cases still occurred.

The relatively small number of cases resulting in serious illness and death were mostly in younger adults and children – particularly those with underlying health problems – and pregnant women.

On August 10 2010, the World Health Organization (WHO) declared the pandemic officially over.

"Swine flu" now

The A/H1N1pdm09 virus is now one of the seasonal flu viruses that circulate each winter. If you've had flu in the last few years, there's a chance it was caused by this virus.

As many people now have some level of immunity to the A/H1N1pdm09 virus, it's much less of a concern than in 2009-10.

The symptoms are the same as normal flu – they're usually mild and pass within a week or so. But as with all types of flu, some people – particularly those with underlying health problems – are at higher risk of serious illness.

The regular flu vaccine will normally protect people at a higher risk of becoming severely ill. A new children's vaccine programme is also being introduced. which aims to protect children and reduce their ability to infect others.